New data from a phase 1 study will be reported at the meeting in Chicago of the American Society of Clinical Oncology (ASCO) by F. Stephen Hodi, MD, director of the Melanoma Treatment Cancer at Dana-Farber on Monday, June 2, 2014.

The trial involved 107 patients with metastatic melanoma that progressed despite several treatments with other therapies. Historically, such patients have a median survival of about 11 months, said Hodi. They received nivolumab between 2008 and 2012. According to his report, the one, two, and three-year overall survival rates are 63 percent, 48 percent, and 41 percent respectively.

“This is the longest follow-up of patients receiving PD-1 blocking drugs in metastatic melanoma in this cohort,” said Hodi, who also heads Dana-Farber’s Center for Immuno-Oncology. “The responses to nivolumab are continuing to be durable with an acceptable safety profile.” He noted that in some cases the benefits have been maintained for more than a year after patients discontinued the drug.

Nivolumab is one of a new class of drugs that target PD-1, a protein on the surface of immune system T cells that restrains them from attacking cancer cells bearing a related protein, PD-L1, on their surface. Nivolumab blocks the action of PD-1, exposing the cancer cells to immune attack.

Of the 107 patients on the trial, 34 (32 percent) had objective responses to nivolumab, meaning their tumors shrank in size: the median duration of the response was 22.9 months. In this group of objective responders, 24 patients stopped nivolumab either because of adverse effects or because they had reached the protocol’s limit of 96 weeks of treatment. After discontinuing the drug, 46 percent of patients maintained their responses for 24 weeks or longer, with some as long as 56 weeks or more.

Analysis of the results suggests that melanoma tumors that express the PD-L1 protein are more likely to respond to nivolumab than tumors that don’t express the protein. This question is being studied in ongoing phase III trials evaluating the role of nivolumab in metastatic melanoma.